Deterioration of underground infrastructure facilities such as sewer pipes poses a serious problem to most developed urban centers today. Sewer pipes form one of the six most capital intensive infrastructure systems in North America. Their poor status has been reported by many researchers, revealing the presence of many defects that impact their performance. It has been documented that the condition of 40% of the total Canadian sewer system has declined over the last ten years. It has also been documented that 68% of the sewer networks of all Canadian municipalities are described as either in need of repair or not acceptable. It has been estimated that Canada needs to spend $5–7 Billion to restore the condition of its sewer network. The decline in the condition of sewer pipes could, generally, be attributed to two main factors: 1) inadequate preventive maintenance and inspection programs and 2) deterioration of pipes. Inadequate maintenance and inspection is mainly attributed to high cost and inadequate funds received from the governmental agencies. Interviews conducted with several municipal engineers and consultants in Quebec and Ontario revealed that the cost of sewer inspection is about CDN $1.5 per linear meter. The breakdown of this cost is about CDN $1.08/m for the production of the video tape and CDN $0.42/m for the inspection of the video tape. Therefore, about 30% of the total cost is spent on inspection of videotapes. This high percentage is attributed to the current inspection practice that is followed by all municipalities. This current practice is performed manually and is fully dependent on human inspectors.
On the other hand, deterioration of pipes could be due to the aging process. As pipes age, they deteriorate and may ultimately fail to fulfill their intended functions. It has been estimated that the average useful life of most commonly used sewer pipes is about 70 years. Most sewer pipes in North America have been in use for the last 40–50 years. Inadequate inspection and maintenance programs accelerate the rate of deterioration of the pipe until it ultimately fails. But, if regular inspection and maintenance programs are conducted, then the performance and lifetime of the pipes can be significantly improved.
Rehabilitation of sewer systems poses a major challenge for most municipalities as they embark on providing quality service and preserving their infrastructure assets. Sewer rehabilitation methods are numerous and are constantly being developed, benefiting from emerging technologies. The implementation of these methods is driven by the need to improve quality, reduce cost and project's duration. One of the rapidly expanding fields in the sewer rehabilitation industry is trenchless technology. Due to the large number of methods associated with emerging new technologies in this field, selecting the most suitable method manually can be a challenging task. Selection in this environment may also suffer from the limited knowledge and/or experience of the decision-maker, and could result in overlooking some of the suitable methods that could do the job at less cost.
Clearly, if sewer pipes inspection process can be automated, then significant time and money can be saved. Automating this process can also provide an incentive for checking this class of pipes more regularly; this will help municipality engineers to plan ahead and avoid unpleasant surprises. Automating the selection process of the most suitable trenchless rehabilitation techniques will also help in saving the construction industry a considerable amount of money. It will also facilitate transfer of knowledge and experience to new engineers who are involved in sewer pipes rehabilitation projects.
Up until recently, inspection of sewer pipes has been a challenging task. The reason is that 95% of this class of pipes is too small for effective manual, i.e. walk-in, inspection. The need to assess the condition of sewer pipes led to the development of new techniques for inspection. In an effort to develop new techniques, the closed-circuit television (CCTV) camera was first introduced in the 1960s. Later on, other techniques were also introduced such as laser-based scanning and ultrasound inspection systems. Despite the development of other inspection techniques, the CCTV inspection remains to be the most commonly used technique by most municipalities.
The process of CCTV inspection is usually accomplished by mounting the camera on a small robot to facilitate its movement in a pipe, or, alternatively, it could be winched between two manholes. As the robot moves along the pipe, the camera scans its inner surface to capture and record any existing defects. This process yields a videotape. This videotape is played back using a VCR and visually inspected to check the structural and serviceability conditions of the inspected pipe. After defects have been identified and classified, a report is prepared and forwarded to an engineer who recommends, based on his own experience, the most suitable rehabilitation techniques.
To protect the investment made in sewer pipes and to safeguard them against sudden collapses, municipalities inspect them using the CCTV camera, and repair them using various techniques. As described earlier, the techniques by which pipes are inspected and methods of repair are selected are currently performed manually. Performing these activities in this manner is usually associated with a number of problems. These problems are highlighted below.
Manual CCTV Inspection Process
The manual CCTV inspection process of sewer pipes suffers from a number of limitations. The following is a description of these limitations and their effects on the overall performance of the process.
Costly: based on various interviews conducted with several municipal engineers and consultants in Quebec and Ontario, it was estimated that the cost of sewer inspection is about CDN $1.5 per linear meter. This total cost can be grouped into two main categories: 1) cost to produce the videotape and 2) cost to inspect the videotape. These categories constitute $1.08/m and $0.42/m of the total cost, respectively. The cost of producing videotapes includes robots, CCTV (closed circuit television) camera, cables, monitors operators and truck. The cost of videotape inspection includes cost of engineers or other trained personnel required to prepare a report on inspected pipes.
Time consuming: While acquiring data (i.e. producing videotapes) takes only few hours, analyzing them is a very time consuming process. The time needed to analyze videotapes is variable, depending on whether the process is conducted in house (i.e. at a municipality) or at a consultant's office. Various municipal engineers and practitioners revealed that if a videotape is analyzed at a consultant's office, then a typical two hour one could take up to two to three weeks to analyze and prepare a report showing types of defects encountered. But, if the analysis process is conducted in house, then one to two days are required to prepare the report of defects.
Tedious: the nature of the inspection process requires inspectors to watch videotapes for long numbers of hours. This is considered a very tedious and boring process for most engineers and practitioners.
Fertile source of diagnostic errors: the process may lead to diagnostic errors due to a lack of concentration of inspectors.
Manual selection of suitable rehabilitation techniques, i.e. not computer assisted, suffers from a number of limitations. The following is a description of these limitations.
Large pool to select from: numerous sewer rehabilitation techniques are available in the market; each is considered suitable for a certain application. Knowing the various limitations and applications of each method is considered a challenge to engineers and practitioners in this field.
Rapidly developing field: due to the rapidly developing nature of the sewer rehabilitation field, evaluating new products as they come available in the market is not performed promptly by municipal engineers and consultants. This is considered as a major drawback that leads to overlooking new products that could do a better job and/or reduce cost.
Overlooking other feasible techniques: the manual selection process, by nature, is heavily dependent on human memory. This could result in overlooking some of the suitable methods that could do the job at less cost and/or better quality.
Localized source of information: usually the decision to be made, as to which rehabilitation technique should be selected, is limited to senior engineers who have good experience in sewer rehabilitation projects. This does not give the opportunity to new engineers to be easily involved in this domain of projects.